The present invention relates to sol or gel compositions capable of enhancing the tannin blocking property of surface coatings and paints, and particularly latex paints applied to outdoor wood surfaces.
References to paints and surface coating compositions are often used interchangeably; however, paints are used to describe pigmented materials as distinct from clear surface coatings such as lacquers or varnishes. The purposes of paint and surface coatings are aesthetic and/or protective. A coating can enhance the appearance of a substrate in terms of colour and gloss as well as give protection against such problems as weathering or corrosion.
Wood is widely used in buildings for such items as roof trusses, timber frames, joists, doors, window frames, cladding and fencing. However, wood is vulnerable to a variety of degrading influences, often caused by weathering, which include light, moisture and biological attachk. A phenomenon of the weathering of wood is the generation of tannins which migrate in the wood. Tannins in wood are essentially derivatives of tannic acid (also called gallotannic phenolics). Tannins, and their migration in wood, can cause visibility of wood grains through inferior wood surface coatings or can cause discoloration of the coating.
In order to block the effects of tannins, a primer surface coating is usually applied to wood, allowed to dry, and then an overcoat is applied. However, the search continues for better overcoats and for surface coating compositions which require only a single coating application and yet effectively block the effects of tannins in wood substrates. To this end, more effective components of coating compositions which serve as tannin blocking agents are presently being sought.